The period of sabbatical training at the Department of Biology, University of California, San Diego, was continued until June 30, 1978. Studies on the function of biological membranes were continued employing the plasma membrane of human red blood cells. The activity of sodium, potassium, adenosine triphosphatase Na (K ions- K ions- Atpase), the enzymatic expression of the principal cation-transport system of eucaryotic cells, was studied particularly in relation to membrane sidedness. Sealed membrane vesicles, oriented right-side-out (RO) or inside-out (IO), were used in order to assess the enzymic interactions at the two membrane surfaces. The techniques employed in this type of work were particularly useful for future research employing parasite membranes and/or membranes of parasitized tissues.